Method of forming a coated metal container and article produced thereby



Dec. 26, 1967 R. B T ET AL 3,360,157

. METHOD OF F ING A ATED METAL CONTAINER AND ARTICLE PRODUCED THEREBY Filed May 4, 1965 2 Sheets-Sheet 1 1; i0 26 /4 Z w .57

74 M U 14 1/ fzamfpzxwsaf k lg/ mweo 205597" .504 r v Edam/QM Dec. 26, 1967 R. .BOLT ET AL 3,360,157

METHOD OF FORM A COATED METAL CONTAINER AND ARTICLE PRODUCED THERE Filed May 4, 1965 2 Sheets-Sheet 2 4% W L 4; 4; 7/25? 4AM 7; f5 M/Z v 5% D114 m 5/ @794 AI ll /l W Z1 M (/5 4 41 if AZ 3.5 g; 1/

a 74 if INVENTORS.

0.4-2 BEE r :auwvo Waaaz e/ r meo eaeaev- 50; r

United States Patent M 3,360,157 METHOD OF FORMING A COATED METAL CON- TAINER AND ARTICLE PRODUCED THEREBY Richard Robert Bolt, Lake Villa, and Delbert Edmund Wobbe, Cary, Ill., assignors to American Can Company, New York, N.Y., a corporation of New Jersey Filed May 4, 1965, Ser. No. 453,017 4 Claims. (Cl. 220-64) ABSTRACT OF THE DISCLOSURE A low carbon steel blank which has been electro-plated with tin having a matte finish is then coated with a suitable oil type lubricant and drawn and ironed into a seamless article, such as a container, the tin coating preventing fracture of the steel by flowing at the ironing die and retaining lubricant through the die, the ironing operation increasing the specularity of the tin to result in an article having a specular side wall.

This invention relates to the manufacture of coated seamless containers and in particular to metal coated steel containers produced by drawing and ironing a precoated blank, without excessive friction.

Many processes are presently being utilized for forming seamless containers from flat blanks. One of these procedures involves first drawing the blank into cup form by forcing the blank through a drawing die by means of a punch mounted upon a press. After drawing, the cup is passed through one or more ironing dies, whose inside diameters are progressively smaller than the outside diameter of the cup.

As drawn, the cup usually has bottom and side wall thicknesses substantially equal to the thickness of the blank. The ironing die thins the side Wall of the drawn cup and forces the metal back, thereby also increasing 'theheight of the container. Additional ironing steps may be added to achieve a desired body Wall thickness and container height.

As used herein, the term drawing may be defined as the forming of recessed parts by forcing the plastic flow of metal in dies, and refers to the operation wherein a peripheral margin of a flat blank is turned inwardly and simultaneously smoothed by means of a drawing punch and die to form a cup having a wrinkle free side wall, whose thickness is substantially equal to the thickness of the original blank. Subsequent redrawing of the cup merely turns up more of the end material in the side wall,

thereby elongating the. side wall, but resulting in, a substantial reduction in the diameter of the cup.

Ironing may be defined as thinning the walls of a deep-drawn article by reducing the clearance between punch and die. In the ironing operation the side wall of the cup is elongated by reducing its thickness with no reduction in the inside diameter of the cup. It is generally accomplished by placing the cup on a closely fitting punch or mandrel and forcing the cup and mandrel through an ironing or reducing die, whose diameter is slightly less than the outer diameter of the cup, thereby forcing the excess metal back and producing a longer but thinner side wall.

Ironing sometimes has been compared to extrusion of metals, since there is an actual squeezing out of the metal. However, the punch pushes the part downwardly resulting in a pulling? of the material in the ironing process. In extrusion, the metal is pushed through a die in the same direction'with the punch. Both processes, however, squeeze the metal.

While the drawing and ironing process has been used extensively in the manufacture of seamless aluminum containers, difficulty has been encountered in utilizing this technique in the manufacture of steel seamless containers. This is thought to be due principally to the fact that steel has much higher tensile and yield strengths and is not as ductile as is aluminum. Since the drawing and ironing process subjects the steel to extreme mechanical deformation, especially during ironing, fracture of the steel and pushing through of the container bottom has frequently been encountered.

Accordingly, an object of the present invention is to provide a method of forming a thin-walled cup-shaped steel container having a thinner side Wall than the end thereof.

Another object is to provide a method of forming a coated, thin-walled, cup-shaped steel container directly from sheet stock.

An additional object is to provide a method for forming a coated steel cup-shaped container having an end thickness equal to and a side wall thickness substantially less than the thickness of the original blank.

A further object is to provide a method of drawing and ironing a steel cup-shaped container without fracture of the metal during drawing and ironing.

A still further object is to provide a method of forming a steel cup-shaped container wherein lubrication during forming may be readily and easily accomplished.

Numerous other objects and advantages of the invention will be apparent as it is better understood from that following description, which, taken in connection with the accompanying drawing, discloses a preferred embodiment thereof.

The above and other object are accomplished by depositing a metal coating which is softer than the basis metal sheet upon which the coating is applied. Thereafter, a blank is provided, by cutting or other-suitable means, from coated basis sheet. The blank is then coated with a suitable oil type lubricant and is placed in a drawing and ironing press. A mandrel then draws the blank into a shallow seamless cup without substantially thinning the end and side wall of the cup. Thereafter, the side wall of the drawn cup is ironed, thus elongating and thinning the side wall while also increasing the specularity of the metal coating on the side Wall as the coating flows and provides lubrication during the ironing. This produces a drawn and ironed one piece coated metal container having an end with the as-deposited soft metal coating thereon and a seamless side Wall Whose thickness is substantially thinner than the end. The side wall of the drawn and ironed metal container has a specular coating thereon brighter than and of the same metal as the as-deposited coating on the end.

Referring to the drawings:

FIGURE 1 is a fragmentary, enlarged, cross-sectional view of the steel sheet having a softer metal coating thereon;

FIGURE 2 is a sectional view of the drawing and ironing die gang and the mandrel used to force the sheet blankthrough the gang;

FIGURES 3 through 5 are fragmentary views, similar to FIGURE 2 showing a blank being formed to a desired container configuration; and

FIGURE 6 is a perspective view of the container parts broken away and partly in section.

As a preferred or exemplary embodiment of the instant invention, a sheet or strip of low carbon, cold-rolled steel is electrolytically coated with a thin layer of tin by means well known to those skilled in the art. This procedure is quite familiar to those knowledgeable in general tin plating for the can-making industry. The thickness of the tin coating may vary considerably depending upon the length and thickness of the final sidewall and the desired thickness of the tin on the final side wall. The final tin thickness must be sufficient to completely cover both surfaces of the final side wall. For example, a coating thickness of approximately 45 microinches be used in the instant process when the thickness of the material is reduced about 50%. Heavier coatings may be utilized but it is preferred that a minimum thickness of tin be used for economic purposes.

For purposes of description, tin will be the metal coating utilized for the steel sheet. However, it has been found that other metals, which are softer than the basis metal, may also be used for the coating. In the case of steel, some of these metals are copper, zinc, brass, nickel, silver, etc. It may be readily understood that other basis metals may also be utilized, the principal criteria being that the metal coating be softer than the basis metal.

As an example of a steel which may be used, the following illustrates a nominal percentage chemical analysis:

Carbon 0.05-0.12 Manganese 0.25-0.60 Sulphur e maximum 0.05 Phosphorus do 0.02 Silicon do 0.10 Copper do 0.20 Iron Balance Typical average mechanical properties of the steel are:

Ultimate tensile strength p.s.i 73,200 Yield strength p.s.i 70,700 Tensile elongation percent 13 Impact elongation do w 1 Hardness 67 R3OT It is readily understood that these are average composition and property values and may vary slightly from melt to melt. Other compositions of steel may also be used without departing from the spirit and scope of the invention, the above steel being used as an example only.

Whereas in general manufacture of electro-tin plate, the tin coating is melted and flow-brightened subsequent to plating, it is preferred in the present invention that no flow brightening take place. Thus, the tin plate is in what is commonly called the matte condition. The reason for this will be more fully explained hereinafter.

FIGURE 1 shows a cross-section of steel 6 with a matte tin deposit 7 covering its surface.

After the electro-tin sheet is dried, a circular blank 8 is cut therefrom by suitable means such as a punch press.

FIGURE 2 shows a gang of dies, generally designated 10, within a die carrier 12. Both the gang 10 and the carrier 12 are mounted in a suitable hydraulic press. An annular die 14 having a die aperture 16 is suitably mounted in the die carrier 12. The die aperture 16 has a rounded drawing face 18 adjacent the upper surface of the die 14.

Reciprocally mounted above the die 14 in axial alignment with the die aperture 16 is a cylindrical forming punch 20 having a lower surface 22. The shape of the end surface 22 determines the endshape of the article to be formed and may be fiat, conical, spheroidal or a combination of these shapes. In the preferred embodiment shown in the drawings, a flat end surface 22 is used for producing flat-ended containers.

The flat circular blank is coated with suitable oil type lubricant which impregnates the matte tin coating 7 and the blank 8 is inserted between the die 14 and an annular blank holder 24 disposed above the die. The blank holder 24 has an inner diameter slightly greater than the diameter of the punch 20 and a spaced series of guide holes 26 extending through the blank holder adjacent the outer edge. Studs 28, having shanks 29 and heads 30, are threadably engaged to the die carrier 12 with the shank portions extending upwardly through the holes 26 in the blank holder 24 to prevent the blank holder from moving transversely relative to the die 14, while permitting it to move upwardly along the longitudinal axis of the die.

Within the lower surface of the blank holder 24, is a circular recess 32 of substantially the same diameter as that of the blank 8 and having a depth which is slightly less than the thickness of the blank, the recess 32 serving to position the blank in axial alignment with the die aperture 16. As thus positioned, the marginal edge 34 of the blank 8 is gripped between the die 14 and the blank holder 24 with a substantial predetermined force due to the action of the compressed springs 36*, disposed about the stud shanks 29 between the blank holder 24 and the stud heads 30. p

The upper end of the punch 20 is attached to a piston rod 38 which in turn is actuated by a suitable power source such as a hydraulic cylinder, which is not shown. Upon actuation, the punch 20 moves downwardly, bringing the lower surface 22 of the punch into contact with the blank 8.

Continuing its downward movement, the punch 20 progressively pulls the marginal edge 34 of the blank 8 from beneath the blank holder 24 and forces it into contact with the drawing face 18 of the die 14. The edge 34 is thus drawn across the drawing face 13 and is stretched and shaped into a tubular configuration to form a side wall 40 of a cup-shaped article having an end 42 (FIGURE 3). At this point both the side wall 40 and the end 42 of the drawn article have thicknesses substantially equal to the thickness of the blank 8.

During the drawing operation, the force with which the marginal edge 34 of the blank 8 is gripped between the blank holder 24 and the die 14 is maintained at a level sufficient to insure that the blank 8 is plastically stretched rather than being wrinkled or folded, as the marginal edge is withdrawn from beneath the blank holder, but is not so great as to result in tearing or cracking of the metal.

Thus the metal is simultaneously subjected to two types of loading in the drawing operation, i.e. a compressive loading on the marginal edge 34 of the blank 8 due to the holding force, and a tension or stretching load on the metal adjacent the drawing face 18 as the metal is drawn from the flat to the tubular form.

Generally, the holding force used will be determined by the particular forming operation. For example, in the drawing and ironing of a 6.125 inch diameter x 0.018 inch thick tin coated steel blank into a 3.285 inch diameter cup having a 0.0008 inch sidewall thickness, a holding force equivalent to approximately 10,000 pounds on the marginaledge of the blank is preferred.

While still being engaged by the drawing face 18, the cup-shaped article enters an annular ironing die 44 mounted in the die holder 12, below the die 14 (FIGURE 4). The ironing die 44 has an ironing face 45 which is smaller than and axially aligned with the drawing face 18 of the die 14. Aspacer plate 46 is disposed between the die 14 and the die 45 to produce a predetermined spacing between the respective dies. The downward movement of the punch 20 forces the tin coated sidewall of the cup shaped article past the ironing face 45, thereby reducing the thickness of and also elongating the sidewall 40.

During this ironing operation, the soft metal coating and the oily lubricant with which it has been impregnated, both serve to lubricate the steel sidewall during its cold reduction. The oil, absorbed on the matte finished plate is held more tenaciously than on conventional flow brightened tin plate, and lubricates better under the extreme ironing pressures encountered. The oil within and upon the tin surface lubricates during the ironing process and the soft coating itself is also burnished and mechanically worked on the outside and stretched on the inside during ironing.

A second ironing die 48 having an ironing face 49 is similarly mounted in die holder 12 below the ironing die 44. A spacer 50 disposed between the ironing dies 44 and 48 produces a predetermined spacing between the respective ironing faces 45 and 49 thereof. As the punch 20 continues downwardly it carries a cup-shaped article into the ironing face 49 while the side wall is still engaged in the ironing face 45 of the first ironing die 44. Depending upon the spacings between the respective ironing faces, the side wall may also still be engaged by the drawing face 18 of the drawing die 14 when it initially enters the ironing face 49 of the second ironing die 48. As it is moved downwardly, the side is then disengaged from the drawing face 18 while still engaged by the ironing faces 45 and 49 of the ironing dies 46 and 48 respectively (FIG- URE 5).

Further ironing of the side wall is done by the ironing face 49 in order to reduce the side wall thickness and increase its length. The drawn and ironed container 52, finally formed, has the end 42 of substantially the same thickness as that of the blank 8 and a side wall 54 whose thickness is substantially less than that of the blank 8. It is to be understood that, While the drawings show only two ironing dies, additional ironing dies may be used to produce any desired side wall length and thickness.

Although the formation of the coated container from the fiat circular blank has been shown as a one-step operation, it is possible to first draw the blank into a shallow seamless cup, and then transfer the cup to another machine containing the ironing dies, where the cup is then forced through the ironing dies in order to thin and also elongate the side Wall.

After passing the second ironing die 48, the continuous downward movement of the punch 20 carries the formed container 52 through a conventional stripper, generally designated 56. The stripper 56 consists of a segmented fiat annular ring 58 having a series of segments 60 adapted to slide radially within a recess 62 in the lower surface of the die holder 12. The segments 60 are urged radially inwardly by springs 64 and are retained within the recess 62 by an annular flat retaining ring 66, secured to the die holder 12 by screws 68. At the extreme inwardly position of the segments 60, the segmented ring 58 has a substantially cylindrical inner surface 70 whose diameter is slightly less than the diameter of the punch 20, With a smoothly rounded upper edge 72 and a sharp lower edge 74.

As the formed container 52 (FIGURE 6) is conveyed toward the stripper 56 by the punch 20, it contacts the rounded upper edge 72 of the segmented ring 58 forcing the segments 60 outwardly to allow the punch and container to pass through the ring. After the container 52 has passed through the ring 58, the springs 64 move the segments 60 inwardly against the punch 20. By suitable means (not shown), the punch 20 is then moved upwardly. During the upward movement of the punch 20, the upper rim 76 of the formed container 52 engages the sharp lower edge 74 of the segmented ring 58. This prevents any further upward movement of the container, thereby stripping it from the punch 20.

It is apparent from the foregoing description of the process that the soft metal coatings on the interior and exterior side walls surfaces of the drawn and iron container are subjected to different mechanical actions. The

internal side wall surface is forced to undergo a 90 degree tensional bend around a curved drawing die and a tensional force during ironing, whereas the exterior side wall surface undergoes a 90 degree compressive bend in the drawing and is then exposed to an extrusion or squeezing action when passing through the ironing dies. On the other hand, the bottom end of the container has not been essentially deformed.

It is also apparent that the exterior coating 7a on the container 52 has undergone a deformation and change different from that of the interior metal coating 7b. With each ironing step, the coating 7a undergoes severe deformation as it is squeezed between the particular ironing face and the mandrel. During this squeezing, the oil that has been impregnated within the soft metal coating 7 on the exterior of the container provides some degree of lubrication for the ironing.

On the other hand, the soft metal coating on the exterior surface of the container flows and is thinned by each succeeding ironing die which reduces the thickness of the side wall 54 and increases its height. The severe mechanical working and burnishing of the coating 7a not only thins the coating and provides lubrication for the ironing operation, but also increases the specularity of the coating until it is brighter than a conventional can made from conventional flow brightened tin plate. Of course, this coating is different than conventional tin plate in that it has not been actually melted and thus-there is no layer of a tin-iron alloy between the tin coating and the steel basis metal as is found in conventional flow brightened or hot dipped tin plate.

Thus, compared to flow brightened tin plate, the asdeposited tin coating provides greater lubrication during the ironing due to its softness and its ability to absorb lubricating oil applied to its surface.

The tin coating 7b on the interior side wall of the container has not been burnished, and therefore, does not exhibit the bright surface characteristics of the exterior coating 7a. As mentioned hereinbefore, the interior side wall coating has only been forced to undergo a degree tensional bend in the drawing operation and then elongation or stretching during ironing period. Thus since it has not been mechanically worked or burnished during the ironing operation, its appearance in generally of the same specularity as it was on the blank, although considerably thinner due to the stretching and the elongating of the side wall.

It should be noted, however, that both the interior and exterior surfaces of the bottom end 42 of the container, which has been neither drawn nor ironed, retain the asdeposited soft metal coating without the brightness of the exterior coating 7a nor the stretched condition of the interior coating 7b.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction, and arrangement of the parts and in the steps of the method described and their order of accomplishment without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form being hereinbefore described being merely a preferred embodiment.

We claim:

1. A method of drawing and ironingan article from a flat blank comprising the steps of:

providing a low carbon steel blank electro-plated with a metal softer and more ductile than said steel, which metal has not been reflowed so that said blank has no alloy layer between said soft metal and said steel;

coating said blank with a lubricant;

forcing said blank through a drawing die to form a shallow cup;

forcing said shallow cup through an ironing die so that the thickness of both said steel and said soft metal is decreased and said side wall is elongated to form said article.

2. A method of drawing and ironing an article from a flat bank comprising the steps of:

providing a low carbon steel blank electro-plated with tin of matte finish having no tin-iron layer between said steel and said tin;

coating said blank with a lubricant;

forcing said blank through a drawing die to form a.

shallow cup;

forcing said shallow cup through an ironing die so that the thickness of both said steel and said tin at the side wall of said cup are decreased, said side wall is elongated to form said article, said tin flows through said ironing die while retaining lubricant to prevent fracture of said steel, and the specularity of said tin increases as it passes through said ironing die.

7 8 3. The method defined in'cla'iin 2" wherein the drawing specular tin on the outer surface thereof and an inand ironing steps are carriedout continuously, by placing tenor coating of matte tin.

said blank over axially aligned drawing and ironing dies and forcing said blank through said dies with a reciprocal References C'ted punch; 5 UNITED" STATES PATENTS 4. A drawn and ironed one-piece tin plated steel con- 2,801,604 8/1957 Russell et a1 113120 tainer comprising: 3,293,895 12/1966 Kohan et a1. 7246 an end having a coating of tin of matte finish; V a seamless side Wall, said side Wall having a thickness THERON CONDON Pr'mary Examiner substantially thinner than said end, and coating of 10 G. T. HALL, Assistant Examiner Disclaimer 3,360,157.Richa1-d Robert Bolt, Lake Villa and Delbert Ed'mlmd Wobbe,

Carry, Ill. METHOD OF FORMIN G A COATED METAL CON- TAINER AND ARTICLE PRODUCED THEREBY. Patent dated Dec. 26, 1967. Disclaimer filed Sept. 4, 1973, by the assignee, American Gan Company. Hereby enters this disclaimer '00 claim 1 of said patent.

[Oficial Gazette December 4, 1973.] 

4. A DRAWN AND IRONED ONE-PIECE TIN PLATED STEEL CONTAINER COMPRISING: AN END HAVING A COATING OF TIN OF MATTE FINISH; A SEAMLESS SIDE WALL, SAID SIDE WALL HAVING A THICKNESS SUBSTANTIALLY THINNER THAN SAID END, AND COATING OF SPECULAR TIN ON THE OUTER SURFACE THEREOF AND AN INTERIOR COATING OF MATTE TIN. 